In many aquifers, the ability to produce water by traditional vertical wells is limited by several factors. In the case of thin aquifers, vertical wells do not allow a long enough section of screen to be installed across the productive formation. This limits the area of the seepage base that can transmit water into the well and reduces the amount of available drawdown that can be created to induce flow toward the well. Both of these factors prevent vertical wells from producing as much water as could be potentially extracted. In other cases, the most productive portion of the aquifer is located under a physical obstruction where a vertical well cannot be installed. These obstructions typically include rivers, lakes, wetlands, structures or other areas where a wellhead is not permitted or access for a vertical drilling rig is impractical.
Horizontal wells are often constructed near or under sources of groundwater recharge, such as rivers, lakes or wetlands. As used herein, “horizontal” well or bore means a well or bore that is not exclusively vertical, but has a substantially horizontal or sub-horizontal portion substantially parallel to the ground surface that allows the horizontal bore to access aquifers of limited depth or to access aquifers blocked from vertical access by obstructions as discussed above. Installing a screen under a source of recharge has the effect of inducing additional recharge to the aquifer. This can substantially increase the sustained yield of a horizontal well by capturing surface water.
Horizontal water supply wells have been traditionally constructed using radial horizontal collector wells, also known as Ranney® type wells. Radial horizontal collector wells are constructed with large vertical caissons, several feet to tens of feet in diameter, installed to the depth of interest. Well screens or casings are jacked or otherwise advanced horizontally from the caisson to the geologic formation. The well screens or casings form horizontal laterals that conduct water from the formation into the caisson where it is pumped to the surface. Building a radial horizontal collector well using this conventional construction technique is a difficult and lengthy undertaking. For this reason, radial horizontal collector wells are often several times the cost of a traditional vertical well. In addition, the laterals cannot generally be steered or directed other than by simple linear protection from the caisson. The method has limited ability to project laterals through boulders, cobbles or other obstruction or difficult drilling conditions.
An additional problem with this conventional construction technique is fluid invasion into the open face of the lateral cannot be controlled during construction. This creates a need to pump significant volumes of water to keep the caissons from flooding during construction. The lateral jacking process usually requires workers to be at the bottom of the caisson. This forces workers to endure wet conditions in a confined space below the water table with all the inherent risks and safety hazards that can occur under such conditions.
Horizontal directional drilling has been used to install utilities such as pipelines and cables, to extract geologic samples, and for various other purposes. These methods involve mud rotary drilling in which the bit enters the ground from a trench or shallow angle from the surface. The bit is directed horizontally as it is pushed from the surface via the drill string. In some recent manifestations, the drill bit can be steered down hole using several cutting heads on a down hole drilling motor. The bit can be steered to direct the bore hole vertically or horizontally. Directionally drilled horizontal holes can be drilled to a point of underground termination. The bit and drill string may then be removed and the well is completed from the opening of the bore hole at the surface. This type of horizontal hole is called a blind hole as the end of the hole is never seen. Horizontal bore holes can also be steered to the surface and terminated above ground. These two sided completions are commonly called continuous bores and allow materials to be introduced into the hole from either side in order to complete construction of, for example, a water supply well.
One known maker of horizontal directional drills is Vermeer Manufacturing Company of Pella, Iowa. Examples of their horizontal directional drills can be seen on their website.
All known existing horizontal directionally drilled bore holes use drilling mud to keep the hole from collapsing, prevent the invasion of large volumes of formation water, remove the cuttings from the bore hole as the drill string advances and provide power and cooling for the down hole drilling motor. The drill muds fall into two major categories, muds based on inorganic clay minerals, such as bentonite, or organic polymers known as biosolid muds. While the use of drilling mud is necessary for the construction of the bore hole, either type of mud produces undesirable effects on the formation around the bore hole. The drilling mud is kept under positive hydraulic head in the bore hole to keep the formation from collapsing. The hydraulic head causes the mud to exfiltrate from the bore hole into the adjacent formation. As it penetrates the formation, the mud creates a zone of invasion which reduces the permeability of the formation adjacent to the bore hole. This has the desirable effect of reducing infiltration of formation water into the bore hole during well construction, but also creates a zone of low permeability that limits the ability of water to flow into the bore hole after construction is completed.
Horizontally directionally drilled bore holes are most commonly used to install cables and pipelines. In these applications, mud invasion of the formation is not a significant concern. However, recently horizontally directionally drilled bore holes have been used to install well screens for environmental remediation wells and for high capacity water supply wells. In these applications, the zone of low permeability created by mud invasion significantly reduces the production capacity of the well. To date, efforts to remove the drilling mud from the invaded zone have proven to be expensive and of only limited effectiveness.
Additional limitations of horizontal directionally drilled borings using drilling muds are commonly encountered. The method has limited ability to prevent collapse of the bore hole in formations containing cobbles and loose gravel. This can cause the formation to collapse on the drilling string. In addition, there is a tendency for cuttings to settle out of the mud forming an obstruction on the bottom of the horizontal portion of the hole. This can also trap the drill string in the hole. Finally, a curved radius of the bore hole is used as a fulcrum to bend the drill string from sub-horizontal to horizontal. In many applications, the formations lack the structural integrity to withstand the stress as the drill rod is forced into the formation at the top of the bore hole. This results in an irregularly shaped bore hole known as a key seat. Key seats can trap the bit in the hole for blind well installations. As a result, grouted casings must be installed across the curved radius of the sub-horizontal portion of the bore hole for longer blind well completions or when dealing with soft formations. This increases the cost and complexity of the drilling operation.
In the drilling of vertical wells, problems of contamination of the area adjacent the well bore by drilling muds has been recognized. Also, where vertical wells have been drilled in earth formations having a high water content, problems have been experienced in extracting water fast enough to effectively advance the drill. In addition, particularly in places where certain shales swell or hydrate in the presence of an influx of water into the well bore, problems have been encountered with the shale becoming loosened and sloughing into the hole necessitating large quantities of shale and cuttings to be lifted out of the well bore. Indeed, if enough shale is loosened, the drill string may even become stuck.
One solution to these problems that has been proposed is using cryogenic gas or liquids as a drilling mud to form a frozen boundary around the vertical bore as it is drilled. Vertical cryogenic drilling methods are described in Maguire, U.S. Pat. No. 3,612,192 and Weaver, U.S. Pat. No. 3,774,701. However, there is no suggestion in these references of the desirability of using vertical cryogenic well drilling techniques for the construction of horizontal bores.
Rebhan, U.S. Pat. No. 4,516,876, describes a tunnel construction technique wherein a pair of vertical caissons are installed at opposite ends of a horizontal tunnel segment. A pilot hole is then drilled between the caissons. A freezing pipe is inserted into the hole and a cooling agent is supplied to the hole to freeze soil adjacent the freeze pipe. Upon creating a freeze zone of sufficient diameter a rotary excavating device rotates around the freezer work pipe to excavate the tunnel. Upon completing excavation of the lengthwise segment of the tunnel, the freezer work pipe is advanced to create a further length of freeze zone and casings can be installed in the newly excavated tunnel. The technique of Rebhan does not allow for construction of cryogenic horizontal wells from the ground surface, nor does it allow the use of directionally controlled drilling equipment.
The present invention is directed toward overcoming one or more of the problems discussed above.